Exploitation method and exploitation well pattern for coalbed methane in low-permeability coalbed

Abstract

An exploitation method and an exploitation well pattern for coalbed methane in a low-permeability coalbed. The method comprises: determining a maximum principal stress direction in a low-permeability coalbed; disposing at least two large-roadway horizontal wells in the low-permeability coalbed; disposing a plurality of production wells on two sides of a horizontal segment of each of the at least two large-roadway horizontal wells, wherein a diameter of each of the production wells is smaller than a diameter of the horizontal segment; exploiting the coalbed methane in the low-permeability coalbed through the at least two large-roadway horizontal wells and the plurality of production wells. Through the horizontal segments of the large-roadway horizontal wells perpendicular to the maximum principal stress direction, it promotes stress release in low-permeability coalbed to form more fracture channels, thereby improving the exploitation efficiency of the coalbed methane in the low-permeability coalbed.

What is claimed is: 
     
       1. An exploitation method for coalbed methane in a low-permeability coalbed, comprising:
 determining a maximum principal stress direction in the low-permeability coalbed, wherein the low-permeability coalbed refers to a coalbed having a permeability lower than a preset permeability; 
 disposing at least two large-roadway horizontal wells in the low-permeability coalbed, wherein each of the large-roadway horizontal wells comprises a vertical segment and a horizontal segment, the horizontal segment is perpendicular to the maximum principal stress direction, and a distance between the horizontal segments of every two adjacent large-roadway horizontal wells in the maximum principal stress direction is within a first preset distance range, and wherein the large-roadway horizontal well refers to a well having a diameter of a horizontal segment within a preset diameter range; 
 disposing a plurality of production wells on two sides of the horizontal segment of each of the at least two large-roadway horizontal wells, wherein a diameter of each of the production wells is smaller than the diameter of the horizontal segment of the large-roadway horizontal well; 
 exploiting the coalbed methane in the low-permeability coalbed through the at least two large-roadway horizontal wells and the plurality of production wells; and 
 wherein the first preset distance range refers to a distance range greater than or equal to 2 kilometers and less than or equal to 4 kilometers, and the preset diameter range refers to a diameter range greater than or equal to 1 meter and less than or equal to 2 meters. 
 
     
     
       2. The method according to  claim 1 , wherein disposing at least two large-roadway horizontal wells in the low-permeability coalbed comprises:
 disposing at least two horizontal wells in the low-permeability coalbed through a wall reinforcing technology and a geosteering technology, wherein each of the horizontal wells comprises a vertical segment and a horizontal segment; and 
 reaming the horizontal segments of the at least two horizontal wells by a high-pressure hydraulic injection method to obtain the at least two large-roadway horizontal wells. 
 
     
     
       3. The method according to  claim 2 , wherein each of the horizontal segments comprised in the at least two large-roadway horizontal wells has a length greater than a preset length. 
     
     
       4. The method according to  claim 3 , wherein the preset length is 600 meters. 
     
     
       5. The method according to  claim 2 , wherein an inter-well distance between any two production wells disposed on a same side of the horizontal segment of each of the large-roadway horizontal wells is within a second preset distance range. 
     
     
       6. The method according to  claim 1 , wherein exploiting the coalbed methane in the low-permeability coalbed through the at least two large-roadway horizontal wells and the plurality of production wells comprises:
 pumping in the at least two large-roadway horizontal wells, respectively, so as to exploit the coalbed methane through the at least two large-roadway horizontal wells; and 
 fracturing the low-permeability coalbed through which each of the plurality of production wells passes, and after the fracturing, pumping in the plurality of production wells, respectively, so as to exploit the coalbed methane through the plurality of production wells. 
 
     
     
       7. The method according to  claim 6 , wherein each of the horizontal segments comprised in the at least two large-roadway horizontal wells has a length greater than a preset length. 
     
     
       8. The method according to  claim 7 , wherein the preset length is 600 meters. 
     
     
       9. The method according to  claim 6 , wherein an inter-well distance between any two production wells disposed on a same side of the horizontal segment of each of the large-roadway horizontal wells is within a second preset distance range. 
     
     
       10. The method according to  claim 1 , wherein the at least two large-roadway horizontal wells can form a plurality of large-roadway horizontal well strings each comprising at least one large-roadway horizontal well, the horizontal segments comprised in the at least one large-roadway horizontal wells are located in a same coalbed, and a distance between the horizontal segments of every two adjacent large-roadway horizontal well strings in the maximum principal stress direction is within the first preset distance range. 
     
     
       11. The method according to  claim 10 , wherein each of the horizontal segments comprised in the at least two large-roadway horizontal wells has a length greater than a preset length. 
     
     
       12. The method according to  claim 11 , wherein the preset length is 600 meters. 
     
     
       13. The method according to  claim 10 , wherein an inter-well distance between any two production wells disposed on a same side of the horizontal segment of each of the large-roadway horizontal wells is within a second preset distance range. 
     
     
       14. The method according to  claim 1 , wherein each of the horizontal segments comprised in the at least two large-roadway horizontal wells has a length greater than a preset length. 
     
     
       15. The method according to  claim 14 , wherein the preset length is 600 meters. 
     
     
       16. The method according to  claim 1 , wherein an inter-well distance between any two production wells disposed on a same side of the horizontal segment of each of the large-roadway horizontal wells is within a second preset distance range. 
     
     
       17. The method according to  claim 1 , wherein each of the at least two large-roadway horizontal wells is L-shaped. 
     
     
       18. An exploitation well pattern for coalbed methane in a low-permeability coalbed, comprising:
 at least two large-roadway horizontal wells each comprising a vertical segment and a horizontal segment, wherein the horizontal segment is perpendicular to a maximum principal stress direction in the low-permeability coalbed, and a distance between the horizontal segments of every two adjacent large-roadway horizontal wells in the maximum principal stress direction is within a first preset distance range, and wherein the large-roadway horizontal well refers to a well having a diameter of a horizontal segment within a preset diameter range, the preset diameter range refers to a diameter range greater than or equal to 1 meter and less than or equal to 2 meters, and the first preset distance range refers to a distance range greater than or equal to 2 kilometers and less than or equal to 4 kilometers; and 
 a plurality of production wells disposed on two sides of the horizontal segment of each of the at least two large-roadway horizontal wells, wherein a diameter of each of the production wells is smaller than the diameter of the horizontal segment of the large-roadway horizontal well. 
 
     
     
       19. The exploitation well pattern for the coalbed methane in the low-permeability coalbed according to  claim 18 , wherein each of the horizontal segments comprised in the at least two large-roadway horizontal wells has a length greater than a preset length. 
     
     
       20. The exploitation well pattern for the coalbed methane in the low-permeability coalbed according to  claim 19 , wherein the preset length is 400 meters, 500 meters or 600 meters. 
     
     
       21. The exploitation well pattern for the coalbed methane in the low-permeability coalbed according to  claim 18 , wherein the at least two large-roadway horizontal wells can form a plurality of large-roadway horizontal well strings each comprising at least one large-roadway horizontal well, the horizontal segments comprised in the at least one large-roadway horizontal wells are located in a same coalbed, and a distance between the horizontal segments of every two adjacent large-roadway horizontal well strings in the maximum principal stress direction is within the first preset distance range. 
     
     
       22. The exploitation well pattern for the coalbed methane in the low-permeability coalbed according to  claim 18 , wherein each of the production wells is a vertical well, an inclined well or a horizontal well. 
     
     
       23. The exploitation well pattern for the coalbed methane in the low-permeability coalbed according to  claim 18 , wherein an inter-well distance between any two production wells disposed on a same side of the horizontal segment of each of the large-roadway horizontal wells is within a second preset distance range, and the second preset distance range refers to a distance range greater than or equal to 100 meters and less than or equal to 600 meters. 
     
     
       24. The exploitation well pattern for the coalbed methane in the low-permeability coalbed according to  claim 23 , wherein the second preset distance range refers to a distance range greater than or equal to 200 meters and less than or equal to 400 meters.